Small Class E PLL Coil
uzzors2k, Mon Jan 28 2008, 07:43PMWhen I started this project I was going to use a half-bridge, but I ruled it out in favour for class E, which I have never tried before. The relatively high frequency of the coil make class E a natural choice, since it will save otherwise huge switching losses and make gate drive easier since only one small gate has to be driven.
The secondary coil itself is 7 cm tall of 0.15mm? windings and 5 cm in diameter. This makes for a self-fres of ~1.35 MHz. For the PLL I used Steve's DWSSTC driver and for power amplification a single BD139/40 gate driver and single IRF630 mosfet was used. I tuned the coil for class E operation yesterday, and during the next few days I will implement audio modulation and an interrupter. Tuning for class E wasn't too difficult, the only problem was the compromise between coupling and proper class E operation. I had to use very low coupling (compared to offline half-bridge SSTCs) in-order not to overdamp the primary LC waveform. Some proof of class E switching is needed of course. Drain and gate voltage are scoped, ignore the ringing, I think my scope is picking up interference from the coil.
Class E really rocks, I can run the coil CW for long periods of time with just a small passive heatsink on the IRF630. Cooling will now be needed for the secondary instead. Some pics of the discharge with 50V supply voltage.
Re: Small Class E PLL Coil
ShawnLG, Mon Jan 28 2008, 11:27PM
I love it. Is your scope display showing two traces? Have you tried secondary current feedback instead of an antenna?
In my attempt to break the smallest SSTC record. I went with class E because of it's simplicity and its ability to work with high frequencies. Getting breakout with only a 2N7000 is difficult.
ShawnLG, Mon Jan 28 2008, 11:27PM
I love it. Is your scope display showing two traces? Have you tried secondary current feedback instead of an antenna?
In my attempt to break the smallest SSTC record. I went with class E because of it's simplicity and its ability to work with high frequencies. Getting breakout with only a 2N7000 is difficult.
Re: Small Class E PLL Coil
Spedy, Tue Jan 29 2008, 12:05AM
Wow, that's really cool. Is class E really that easy for the power output? It looks fantastic. Good job.
Spedy, Tue Jan 29 2008, 12:05AM
Wow, that's really cool. Is class E really that easy for the power output? It looks fantastic. Good job.
Re: Small Class E PLL Coil
flannelhead, Tue Jan 29 2008, 01:22PM
That's a real beauty!!
I'm also going to make something similar. It's gonna be powered from 12v lead acid battery. The secondary is wound on a film canister (3.1 cm diameter, winding length 4.5 cm) with 0.1mm wire. I'll be most likely using PLL. Let's see what can I get out of that!!
BTW, would a IRFP240 or IRF540 be fine with that kind of a circuit?
flannelhead, Tue Jan 29 2008, 01:22PM
That's a real beauty!!
I'm also going to make something similar. It's gonna be powered from 12v lead acid battery. The secondary is wound on a film canister (3.1 cm diameter, winding length 4.5 cm) with 0.1mm wire. I'll be most likely using PLL. Let's see what can I get out of that!!
BTW, would a IRFP240 or IRF540 be fine with that kind of a circuit?
Re: Small Class E PLL Coil
uzzors2k, Tue Jan 29 2008, 02:40PM
Thanks. The oscilliogram is dual trace, with both drain and gate voltage shown simultaneously. It was taken with 12V test voltage, but the waveforms don't differ much at 50V. I haven't tried base current feedback yet, but I plan to do so soon. Antenna are just trouble when boxing up SSTCs. I can't recall your class E coil, did you make a thread about it or is it "unofficial"?
Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.
uzzors2k, Tue Jan 29 2008, 02:40PM
Thanks. The oscilliogram is dual trace, with both drain and gate voltage shown simultaneously. It was taken with 12V test voltage, but the waveforms don't differ much at 50V. I haven't tried base current feedback yet, but I plan to do so soon. Antenna are just trouble when boxing up SSTCs. I can't recall your class E coil, did you make a thread about it or is it "unofficial"?
Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.
Re: Small Class E PLL Coil
ragnar, Tue Jan 29 2008, 03:26PM
**shameless hijack, because my thread of the same topic was ignored months ago**
ragnar, Tue Jan 29 2008, 03:26PM
**shameless hijack, because my thread of the same topic was ignored months ago**
Re: Small Class E PLL Coil
Tom540, Tue Jan 29 2008, 08:30PM
thats because hijackers are ignored, lol.
Tom540, Tue Jan 29 2008, 08:30PM
Matt Bingham wrote ...
**shameless hijack, because my thread of the same topic was ignored months ago**
**shameless hijack, because my thread of the same topic was ignored months ago**
thats because hijackers are ignored, lol.
Re: Small Class E PLL Coil
flannelhead, Wed Jan 30 2008, 01:39PM
Yep, the frequency will be high (calculated with javatc ~2.5 MHz). And that's why I'm gonna use 74HC4046 instead of the normal CD4046. Its output current/pin is 25mA, so I'll need a 220 ohm resistor from the VCO out to the BD139/40 bases, right? (I'm going to drive the circuitry with 5V, except 12V to the BD139 collector). Or could the VCO output (pin 4) be connected straight to the bases?
EDIT: One more question, what is thet 10R resistor on top of the dwsstc II schematic for? I can't see any reason for that. I suppose it can be left out if I use 74HC4046?
flannelhead, Wed Jan 30 2008, 01:39PM
Uzzors wrote ...
Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.
Class E requires very few parts, and is quite elegant. Tuning for proper class E switching is the only critical portion, and even that is easy. (A scope is required though) With a film can secondary the fres will be pretty high, so mosfets with small delays and capacitances are needed. Those mosfets should be fast enough Spark, and their gate charge isn't very large either. Try them and see! If you need IRF630s I've found piles of them in monitors.
Yep, the frequency will be high (calculated with javatc ~2.5 MHz). And that's why I'm gonna use 74HC4046 instead of the normal CD4046. Its output current/pin is 25mA, so I'll need a 220 ohm resistor from the VCO out to the BD139/40 bases, right? (I'm going to drive the circuitry with 5V, except 12V to the BD139 collector). Or could the VCO output (pin 4) be connected straight to the bases?
EDIT: One more question, what is thet 10R resistor on top of the dwsstc II schematic for? I can't see any reason for that. I suppose it can be left out if I use 74HC4046?
Re: Small Class E PLL Coil
uzzors2k, Thu Jan 31 2008, 05:58PM
You had your thread, Matt
, but if your self esteem needs a boost be my guest... Beautiful coil Matt! 
I think the 10 ohm resistor might be there to improve voltage regulation for the 4046. Being a VCO the frequency will be sensitive to supply fluctuations. Other than that I'm not sure what it's for, and I don't use one myself. 25mA isn't enough to drive the BD's hard enough to drive the main mosfet with good rise/fall times. I would use a 4049 buffer chip to take the strain off the PLL and supply enough current to the BDs. At 2.5MHz I don't know how well the BDs will hold up, even with a minuscule capacitance like the IRF630 has. You might want to use a gate drive chip, a really small, fast mosfet, or some better gate drive transistors.
uzzors2k, Thu Jan 31 2008, 05:58PM
You had your thread, Matt
, but if your self esteem needs a boost be my guest... Beautiful coil Matt! I think the 10 ohm resistor might be there to improve voltage regulation for the 4046. Being a VCO the frequency will be sensitive to supply fluctuations. Other than that I'm not sure what it's for, and I don't use one myself. 25mA isn't enough to drive the BD's hard enough to drive the main mosfet with good rise/fall times. I would use a 4049 buffer chip to take the strain off the PLL and supply enough current to the BDs. At 2.5MHz I don't know how well the BDs will hold up, even with a minuscule capacitance like the IRF630 has. You might want to use a gate drive chip, a really small, fast mosfet, or some better gate drive transistors.
Re: Small Class E PLL Coil
Steve Conner, Thu Jan 31 2008, 06:48PM
I put the 10 ohm resistor there, together with a capacitor to ground, to try and keep noise out of the 4046. I don't know whether it's needed or not. I read that the 4046 is sensitive to supply voltage variations, so I took that to mean dynamically as well as statically.
Steve Conner, Thu Jan 31 2008, 06:48PM
I put the 10 ohm resistor there, together with a capacitor to ground, to try and keep noise out of the 4046. I don't know whether it's needed or not. I read that the 4046 is sensitive to supply voltage variations, so I took that to mean dynamically as well as statically.
Re: Small Class E PLL Coil
uzzors2k, Thu Feb 14 2008, 07:24PM
I switched over to secondary base current feedback, added an interrupter and soldered up a board. This was done two weeks ago now, but due to a lack of Internet connection and a different project I haven't gotten around to keeping you guys in the loop. The other project is a power supply for this thing which I hope to finish soon so I can wrap this coil up.
uzzors2k, Thu Feb 14 2008, 07:24PM
I switched over to secondary base current feedback, added an interrupter and soldered up a board. This was done two weeks ago now, but due to a lack of Internet connection and a different project I haven't gotten around to keeping you guys in the loop. The other project is a power supply for this thing which I hope to finish soon so I can wrap this coil up.
Re: Small Class E PLL Coil
Arcstarter, Thu Feb 14 2008, 07:39PM
wow great coil!its tiny yet powerful.the minimight!i hope i didnt steal that name from somewhere..
Arcstarter, Thu Feb 14 2008, 07:39PM
wow great coil!its tiny yet powerful.the minimight!i hope i didnt steal that name from somewhere..
Re: Small Class E PLL Coil
flannelhead, Fri Feb 15 2008, 07:25AM
That's pretty nice!
Have you tried audio modulation yet?
I hope I'll finish my 12v coil soon!
BTW, where did you get the current transformer core? And how many turns did you wind?
flannelhead, Fri Feb 15 2008, 07:25AM
That's pretty nice!
Have you tried audio modulation yet?
I hope I'll finish my 12v coil soon!
BTW, where did you get the current transformer core? And how many turns did you wind?
Re: Small Class E PLL Coil
uzzors2k, Fri Feb 15 2008, 01:25PM
Thanks for the compliments. I forgot to mention that I added audio modulation as well. The streamer hisses a lot so the sound quality isn't great, but it works. The first time I tried audio modulation I sat and enjoyed it so long that the breakout point melted through the top of the former! That only took about 2 minutes, so audio modulation won't be used very often with this coil. The secondary itself was warm at this point too.
You can sort of see the transformer core in the picture, I just grabbed it from an ATX supply. I don't think the turns count is very critical, say about 30.
uzzors2k, Fri Feb 15 2008, 01:25PM
Thanks for the compliments. I forgot to mention that I added audio modulation as well. The streamer hisses a lot so the sound quality isn't great, but it works. The first time I tried audio modulation I sat and enjoyed it so long that the breakout point melted through the top of the former! That only took about 2 minutes, so audio modulation won't be used very often with this coil. The secondary itself was warm at this point too.
You can sort of see the transformer core in the picture, I just grabbed it from an ATX supply. I don't think the turns count is very critical, say about 30.
Re: Small Class E PLL Coil
CT2, Fri Feb 15 2008, 10:13PM
For the secondary base feedback, that transformer is it the little yellow toroid one thats on the output, I think its for current sensing? If it is did you even rewind it or just use it as is? That'll be sweet if its that easy to get good secondary feedback.
CT2, Fri Feb 15 2008, 10:13PM
For the secondary base feedback, that transformer is it the little yellow toroid one thats on the output, I think its for current sensing? If it is did you even rewind it or just use it as is? That'll be sweet if its that easy to get good secondary feedback.
Re: Small Class E PLL Coil
Experimentonomen, Sat Feb 16 2008, 09:53AM
CT2, if you mean the yellow one with white rim on the output of computer power supplies, then the answer is no, you cannot use these as current transformers since they are iron powder cores indended for dc filter operation.
Experimentonomen, Sat Feb 16 2008, 09:53AM
CT2, if you mean the yellow one with white rim on the output of computer power supplies, then the answer is no, you cannot use these as current transformers since they are iron powder cores indended for dc filter operation.
Re: Small Class E PLL Coil
uzzors2k, Sat Feb 16 2008, 10:41AM
It was used a a CT in the power supply and I used it as is. If it has one turn going through it which is in series with the main transformer it's the right one. I've found them connected to the base drive transformer too, but it's primary will still be in series with the main power transformer no matter where it is. The only yellow toroids I can recall are the huge filter inductors, which are unsuitable. Pretty much every ATX psu I have come across has had a CT for short circuit sensing.
uzzors2k, Sat Feb 16 2008, 10:41AM
It was used a a CT in the power supply and I used it as is. If it has one turn going through it which is in series with the main transformer it's the right one. I've found them connected to the base drive transformer too, but it's primary will still be in series with the main power transformer no matter where it is. The only yellow toroids I can recall are the huge filter inductors, which are unsuitable. Pretty much every ATX psu I have come across has had a CT for short circuit sensing.
Re: Small Class E PLL Coil
Experimentonomen, Sat Feb 16 2008, 03:13PM
I rarely see power supplies with ct ocd
Experimentonomen, Sat Feb 16 2008, 03:13PM
I rarely see power supplies with ct ocd
Re: Small Class E PLL Coil
CT2, Sat Feb 16 2008, 06:48PM
HFsstc-freak I know the big toroid on the output cannot be used for this application, but I wasn't referring to that one. Uzzors is this the same toroid that you used? It currently has 20 turns on it, I didn't think that was enough but you said you didn't modify it?
CT2, Sat Feb 16 2008, 06:48PM
HFsstc-freak I know the big toroid on the output cannot be used for this application, but I wasn't referring to that one. Uzzors is this the same toroid that you used? It currently has 20 turns on it, I didn't think that was enough but you said you didn't modify it?
Re: Small Class E PLL Coil
uzzors2k, Sun Feb 17 2008, 08:57AM
That's the type CT2. Since the input of the 4046 is very sensitive and has a high impedance almost any turns ratio will work. I measured the signal at the input and it was only 1Vp-p IIRC. Since I doubted such a weak signal could actually provide feedback I disconnected the CT only to find I couldn't tune the coil anymore, so it definitely works. I didn't use a burden resistor, just two 1N4148s to clamp the signal (just in case) and a 10nF cap from there to the input of the 4046. I guess it's about time for a schematic.
uzzors2k, Sun Feb 17 2008, 08:57AM
That's the type CT2. Since the input of the 4046 is very sensitive and has a high impedance almost any turns ratio will work. I measured the signal at the input and it was only 1Vp-p IIRC. Since I doubted such a weak signal could actually provide feedback I disconnected the CT only to find I couldn't tune the coil anymore, so it definitely works. I didn't use a burden resistor, just two 1N4148s to clamp the signal (just in case) and a 10nF cap from there to the input of the 4046. I guess it's about time for a schematic.
Re: Small Class E PLL Coil
uzzors2k, Sun Mar 09 2008, 07:48PM
I spent all of today building a plexiglas box for the coil, only to test the coil and find that it won't break out anymore!
I have no idea what's wrong with it, and troubleshooting all afternoon has only given me a dead IRF630. The supply voltage to the 4046 has changed, so hopefully it's just a major tuning issue...
uzzors2k, Sun Mar 09 2008, 07:48PM
I spent all of today building a plexiglas box for the coil, only to test the coil and find that it won't break out anymore!
I have no idea what's wrong with it, and troubleshooting all afternoon has only given me a dead IRF630. The supply voltage to the 4046 has changed, so hopefully it's just a major tuning issue...
Re: Small Class E PLL Coil
flannelhead, Mon Mar 10 2008, 01:24PM
Looks so cool! Hopefully you get it working!
I didn't feel like making a box for my sstc. It doesn't seem to be worth it and now the coil is broken
BTW, how's your auxiliary power supply project going? Are you going to finish it and use it with this coil?
flannelhead, Mon Mar 10 2008, 01:24PM
Looks so cool! Hopefully you get it working!
I didn't feel like making a box for my sstc. It doesn't seem to be worth it and now the coil is broken
BTW, how's your auxiliary power supply project going? Are you going to finish it and use it with this coil?
Re: Small Class E PLL Coil
uzzors2k, Thu Mar 13 2008, 08:06PM
Done!
I swapped the '630 for a 'P450, and changed capacitor values and CT phasing numerous times to get it tuned again. It seems to be working well finally, so I think it can be shelved once and for all. The plexiglas work doesn't compare to Christopher's magic, but being the first time I've used the stuff I'm satisfied. It can run from 35- 50V, so if I ever feel for it I can make an external power supply. I gave up on the previous PSU project weeks ago.
uzzors2k, Thu Mar 13 2008, 08:06PM
Done!
I swapped the '630 for a 'P450, and changed capacitor values and CT phasing numerous times to get it tuned again. It seems to be working well finally, so I think it can be shelved once and for all. The plexiglas work doesn't compare to Christopher's magic, but being the first time I've used the stuff I'm satisfied. It can run from 35- 50V, so if I ever feel for it I can make an external power supply. I gave up on the previous PSU project weeks ago.
Re: Small Class E PLL Coil
..., Thu Mar 13 2008, 10:23PM
That coil looks awesome!
heh, making plexiglass look nice is way harder than it looks. For my coil I ended up build the base of the coil out of some hardwood and using plexi just for a clear top so you can see what is inside
..., Thu Mar 13 2008, 10:23PM
That coil looks awesome!
heh, making plexiglass look nice is way harder than it looks. For my coil I ended up build the base of the coil out of some hardwood and using plexi just for a clear top so you can see what is inside
Re: Small Class E PLL Coil
flannelhead, Fri Mar 14 2008, 02:21PM
What do you use for rf ground? Is it just mains ground?
flannelhead, Fri Mar 14 2008, 02:21PM
What do you use for rf ground? Is it just mains ground?
Re: Small Class E PLL Coil
uzzors2k, Fri Mar 14 2008, 03:55PM
Plain old mains ground. This coil is so small it shouldn't be a problem and it hasn't been one so far. My PSU provides filtering.
uzzors2k, Fri Mar 14 2008, 03:55PM
Plain old mains ground. This coil is so small it shouldn't be a problem and it hasn't been one so far. My PSU provides filtering.
Re: Small Class E PLL Coil
flannelhead, Mon Mar 17 2008, 02:00PM
Your coil looks so sweet that I'm gonna clone it (well, almost.)
About the class-E, is the resonant cap size same that it would be in a SGTC? Or is this completely different stuff?
Is it fine to use polyester caps?
flannelhead, Mon Mar 17 2008, 02:00PM
Your coil looks so sweet that I'm gonna clone it (well, almost.)
About the class-E, is the resonant cap size same that it would be in a SGTC? Or is this completely different stuff?
Is it fine to use polyester caps?
Re: Small Class E PLL Coil
Dr. H., Mon Mar 17 2008, 02:34PM
Thats some sweet coil Uzzors
. What is the maximum spark lenght that you could pull from it ?
Cheers Huben
Dr. H., Mon Mar 17 2008, 02:34PM
Thats some sweet coil Uzzors
. What is the maximum spark lenght that you could pull from it ?Cheers Huben
Re: Small Class E PLL Coil
uzzors2k, Mon Mar 17 2008, 04:53PM
Thanks. I never measured the spark length but it looks to be about half the coil's length, so 4 cm.
Spark; It's hard to determine the capacitor size before experimenting, so just buy a bunch of smaller caps with a sum of about 3nF. 220pF increments are good for adjusting. I used 660pF with an IRFP450 and 2nF with a '630. It will ultimately depend on frequency, primary inductance and peak voltage though. Polyester caps should do fine.
uzzors2k, Mon Mar 17 2008, 04:53PM
Thanks. I never measured the spark length but it looks to be about half the coil's length, so 4 cm.
Spark; It's hard to determine the capacitor size before experimenting, so just buy a bunch of smaller caps with a sum of about 3nF. 220pF increments are good for adjusting. I used 660pF with an IRFP450 and 2nF with a '630. It will ultimately depend on frequency, primary inductance and peak voltage though. Polyester caps should do fine.
Re: Small Class E PLL Coil
flannelhead, Tue Mar 18 2008, 01:00PM
Ok. I'll try to get it tuned right.
So, it's gonna be kinda small and I want the power supply to be small. I thought about those laptop computer battery chargers... They can put out some 20V@3A, and they are quite small. I just have to think where I can get one.
flannelhead, Tue Mar 18 2008, 01:00PM
Ok. I'll try to get it tuned right.
So, it's gonna be kinda small and I want the power supply to be small. I thought about those laptop computer battery chargers... They can put out some 20V@3A, and they are quite small. I just have to think where I can get one.
Re: Small Class E PLL Coil
101111, Tue Mar 18 2008, 01:09PM
I've actually built a very small class-E Tesla coil based on Steve's PLL driver. It looks very like Uzzors but it is a little smaller.
I'll make a thread about it when I manages to find my camera.
Nice coil btw Uzzors..
EDIT 08.03.09: For those who are curious. *arrogant :p * my coil never worked...
101111, Tue Mar 18 2008, 01:09PM
I've actually built a very small class-E Tesla coil based on Steve's PLL driver. It looks very like Uzzors but it is a little smaller.
I'll make a thread about it when I manages to find my camera.
Nice coil btw Uzzors..
EDIT 08.03.09: For those who are curious. *arrogant :p * my coil never worked...
Re: Small Class E PLL Coil
Anubisbot-HV, Sat Aug 30 2008, 04:44PM
Hi,
tis coil is so nice , i want it to be my first coil i want to make.
Since it has audio in and it runs from low voltage, it seems to be the best chioce.
Sorry when my english is not that good , i am german, so be kind:)
Uzzors do u have a final shematik for me what i coud use to make PCB, since i have still a job good at the PCB factory.
And i want to make a setup with 4 of those running Suround sound. ok bass is some sort of a broblem.
And how about power consumtion? U used 35-50 V would it be posible touse 12V or 24V ? i have a computer regulated power supply, do i need some kind of prtection for power spikes back to my supply??
I know a lot of questions?
Best regards Anubisbot
Anubisbot-HV, Sat Aug 30 2008, 04:44PM
Hi,
tis coil is so nice , i want it to be my first coil i want to make.
Since it has audio in and it runs from low voltage, it seems to be the best chioce.
Sorry when my english is not that good , i am german, so be kind:)
Uzzors do u have a final shematik for me what i coud use to make PCB, since i have still a job good at the PCB factory.
And i want to make a setup with 4 of those running Suround sound. ok bass is some sort of a broblem.
And how about power consumtion? U used 35-50 V would it be posible touse 12V or 24V ? i have a computer regulated power supply, do i need some kind of prtection for power spikes back to my supply??
I know a lot of questions?
Best regards Anubisbot
Re: Small Class E PLL Coil
uzzors2k, Sun Aug 31 2008, 01:30PM
By tuning the primary you can use any supply voltage you want, at any power level. Simply play with the number of turns, coupling and so forth. The audio modulation of my coil is far below satisfactory because the PLL oscillates too much. If you want good sound quality I would recommend Reaching's coil instead. For the first it uses a crystal so the nothing will be oscillating in the audio range, and secondly it modulates the power to the coil giving excellent audio quality.
uzzors2k, Sun Aug 31 2008, 01:30PM
By tuning the primary you can use any supply voltage you want, at any power level. Simply play with the number of turns, coupling and so forth. The audio modulation of my coil is far below satisfactory because the PLL oscillates too much. If you want good sound quality I would recommend Reaching's coil instead. For the first it uses a crystal so the nothing will be oscillating in the audio range, and secondly it modulates the power to the coil giving excellent audio quality.
Re: Small Class E PLL Coil
..., Sun Aug 31 2008, 05:30PM
It is very possible to audiomodulate a pll coil, although I have found it works best to disable the PLL (easily done by grounding the antenna or not passing the primary through the current transformers depending on your topology) and just use it as a VCO. You can adjust the volume level by changing the high/low frequinecy limit resistors. The only problem with this method is that there is a relativley limited amount of modulation available. My coil running about 500w is loud enough to fill a decent size room (ie classroom) with audio no problem, but a little tiny coil could struggle to produce good sounding audio at high volume levels. I should point out that once you get the circuit all tuned up the audio actually sounds very good, even at my downright low 700KHz operating frequinecy the audio was about as good as my laptop speakers, although there is a lot of hiss. It isn't so much static like you would hear from an untuned radio, but more just it is harder to hear anything in the room because the their is more noise.
..., Sun Aug 31 2008, 05:30PM
It is very possible to audiomodulate a pll coil, although I have found it works best to disable the PLL (easily done by grounding the antenna or not passing the primary through the current transformers depending on your topology) and just use it as a VCO. You can adjust the volume level by changing the high/low frequinecy limit resistors. The only problem with this method is that there is a relativley limited amount of modulation available. My coil running about 500w is loud enough to fill a decent size room (ie classroom) with audio no problem, but a little tiny coil could struggle to produce good sounding audio at high volume levels. I should point out that once you get the circuit all tuned up the audio actually sounds very good, even at my downright low 700KHz operating frequinecy the audio was about as good as my laptop speakers, although there is a lot of hiss. It isn't so much static like you would hear from an untuned radio, but more just it is harder to hear anything in the room because the their is more noise.
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